The purpose of the proposed research project will be to study cell-to-cell communication via gap junctions between myocardial cells in culture and also between embryonic and differentiating cells. This objective will be pursued by developing appropriate biochemical, immunological, and genetic approaches: isolated gap junctions will be characterized biochemically; junction-specific antisera will be prepared; and communication-defective mutants will be isolated. These approaches will then be applied to study some specific gap junction problems. These include studies on: the molecular basis for low-resistance communication; the relationship between junctional structure and permeability in myocardial cell cultures; the disruption and biogenesis of gap junctions in vivo; and the the biological role of communication in developing systems. Recent progress in biosynthesis and immunology have permitted an expansion of the program in these areas.